The present invention relates to a printing head of an impact type printer. More particularly, it is concerned with a printing head of a cancel type printer wherein a strain energy stored by an attraction of a permanent magnet is released to an attraction member by a cancellation thereof.
Printing heads for impact type printers are of the so-called magnetic drive type in which an attraction member is accelerated for printing operations by attraction of an electromagnet or of the so-called cancel type in which a spring member is displaced by attraction of a permanent magnet to thereby impart a strain energy to the spring member so that the attraction of the permanent magnet is cancelled by magnetic flux of the electromagnet for the printing operation.
Since the above described cancel type printing head possesses various advantages over the magnetic drive type printing head, various kinds of cancel type printing heads are widely used at present.
In such a type of printing head, the printing wire or the attraction member coupled thereto is moved by the strain energy stored by the displacement of the spring member. In other words, the resilient force of the spring member is directly used as a printing energy of the printing wire so that the printing quality depends mainly on variation of the resilient force of the spring member with respect to a set value.
However, in the conventional cancel type printing heads, one end of the spring member is fixedly secured to the head body or the like. For this reason, the resilient force of the spring member must be adjusted by the magnetic flux of the permanent magnet or the exerted magnetic force of the electromagnet or a machining allowance of the spring member must be strictly limited. This is disadvantageous in that it is very difficult to manage the production process of the spring member, thereby maintaining a satisfactory mechanical allowance and to adjust the spring force of the spring member.